The present invention generally relates to noise monitoring apparatus and in particular to an apparatus for detecting maximum noise levels and dosages and for accumulating data relating to noise dosages.
There is substantial concern for the hearing of workers exposed to noisy environments. Most of the work in this area has been done on devices for protecting the hearing such as ear plugs and external ear muffs. Such devices operate by attenuating the intensity of the noise transmitted through them. In general, the higher frequency components are attenuated more than the lower frequency components. However, in order to protect against extremely high noise intensities, these devices require bulky and expensive construction.
One method of reducing the size of the hearing protector is to include an electronic noise limiter. In one prior art apparatus, all sounds must pass through an electro-acoustical transmission system. This system includes means for limiting the maximum excursion of the amplitude of the noise signals to a predetermined safe level.
One problem with such noise limiting devices is that there is no record of the total noise exposure of the worker during his shift. If the worker is subject to noise dosage standards such as noise intensity over predetermined time periods, the work time must be limited to the standard period for the maximum noise limit of the limiting means. Depending upon the actual noise levels the worker has received, the worker may be required to stop work before he receives the maximum allowable dosage. One solution to this problem is in the form of a noise monitoring circuit mounted on a "hard" hat. A microphone and a battery pack is located on one side of the hat and a noise dosimeter is located on the other side of the hat. The dosimeter includes storage for noise levels over 115 dBA and a memory cell built to OSHA (Occupational Safety and Health Administration) criteria.